Then Baalke stopped playing coy. Flowers, after all, visited the 49ers in June before he signed with the Chargers. Baalke said the team was merely kicking the tires on Flowers, who made 17 interceptions in six seasons with Kansas City and returned three for touchdowns.

"Anytime there are players out there - we've said this often - we reach out, we do our due diligence, we look into every acquisition that could be made," Baalke said. "But we feel good about the group we have. We really do."

Perhaps. But the 49ers' interest in Flowers could be a nod to the question marks dotting their cornerback corps beyond likely season-opening starters Tramaine Brock and Chris Culliver.

If Brock or Culliver were sidelined, the 49ers would turn to ...

-- Perrish Cox? The four-year veteran hasn't started a game since his rookie season and was released three times - twice by the Seahawks - last year.

-- Chris Cook? The free-agent signee - a 2010 second-round pick who was a disappointment in Minnesota - hasn't had an interception in 29 career starts.

It's easy to see why depth at the cornerback spot could be a concern for a team that will face six of the quarterbacks who ranked among the NFL's top eight in passer rating last season.

On Saturday, head coach Jim Harbaugh said Brock and Culliver were at a "different level" than the other cornerbacks. First-round pick Jimmie Ward is working at slot cornerback. Cox, Cook, Johnson and Acker? Time will tell.

"They are all just working," Harbaugh said "They're working to assert themselves."

Of that group, Cook is the most intriguing. At 6-foot-2 and 212 pounds, he has the long-armed, rangy build currently en vogue at the position. The No. 34 overall pick in 2010, Cook, the 49ers hope, will be the latest high-end draft pick to realize his potential under the tutelage of secondary coach Ed Donatell.

Two 2011 free-agent signees - cornerback Carlos Rogers and safety Donte Whitner - were top-10 picks who made their first Pro Bowls with the 49ers.

For Cook to enjoy a similar career renaissance, he must improve in an area that helps explain his zero career interceptions. In June, defensive coordinator Vic Fangio said Cook has had issues locating the ball.

"When the ball's thrown up, you've got to be able to find the ball and make a play at the ball," Fangio said. "And he's struggled there in his past. So, whatever we can do to improve him in that area will go a long way in helping his career."

Cook clearly has received the message. He spent part of his month away from the team before training camp in his native Virginia working on that weakness. Cook enlisted a quarterback and wide receiver so he could practice turning his head while maintaining tight coverage.

"It's repetition," Cook said. "... It's just tracking the ball in the air. And just beat at it and chip at it until it gets better."